Implications of Warm Rain in Shallow Cumulus and Congestus Clouds for Large-Scale Circulations
Space-borne observations reveal that 20–40% of marine convective clouds below the freezing level produce rain. In this paper we speculate what the prevalence of warm rain might imply for convection and large-scale circulations over tropical oceans. We present results using a two-column radiative–con...
| Main Authors: | , , , |
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| Other Authors: | |
| Format: | Article |
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Springer-Verlag
2018
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| Online Access: | http://hdl.handle.net/1721.1/118189 https://orcid.org/0000-0002-2066-2082 |
| _version_ | 1826206967776935936 |
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| author | Nuijens, Louise Masunaga, Hirohiko L’Ecuyer, Tristan Emanuel, Kerry Andrew |
| author2 | Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences |
| author_facet | Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences Nuijens, Louise Masunaga, Hirohiko L’Ecuyer, Tristan Emanuel, Kerry Andrew |
| author_sort | Nuijens, Louise |
| collection | MIT |
| description | Space-borne observations reveal that 20–40% of marine convective clouds below the freezing level produce rain. In this paper we speculate what the prevalence of warm rain might imply for convection and large-scale circulations over tropical oceans. We present results using a two-column radiative–convective model of hydrostatic, nonlinear flow on a non-rotating sphere, with parameterized convection and radiation, and review ongoing efforts in high-resolution modeling and observations of warm rain. The model experiments investigate the response of convection and circulation to sea surface temperature (SST) gradients between the columns and to changes in a parameter that controls the conversion of cloud condensate to rain. Convection over the cold ocean collapses to a shallow mode with tops near 850 hPa, but a congestus mode with tops near 600 hPa can develop at small SST differences when warm rain formation is more efficient. Here, interactive radiation and the response of the circulation are crucial: along with congestus a deeper moist layer develops, which leads to less low-level radiative cooling, a smaller buoyancy gradient between the columns, and therefore a weaker circulation and less subsidence over the cold ocean. The congestus mode is accompanied with more surface precipitation in the subsiding column and less surface precipitation in the deep convecting column. For the shallow mode over colder oceans, circulations also weaken with more efficient warm rain formation, but only marginally. Here, more warm rain reduces convective tops and the boundary layer depth—similar to Large-Eddy Simulation (LES) studies—which reduces the integrated buoyancy gradient. Elucidating the impact of warm rain can benefit from large-domain high-resolution simulations and observations. Parameterizations of warm rain may be constrained through collocated cloud and rain profiling from ground, and concurrent changes in convection and rain in subsiding and convecting branches of circulations may be revealed from a collocation of space-borne sensors, including the Global Precipitation Measurement (GPM) and upcoming Aeolus missions. Keywords: Warm rain; Shallow cumulus; Congestus; Circulations; Climate |
| first_indexed | 2024-09-23T13:41:25Z |
| format | Article |
| id | mit-1721.1/118189 |
| institution | Massachusetts Institute of Technology |
| last_indexed | 2024-09-23T13:41:25Z |
| publishDate | 2018 |
| publisher | Springer-Verlag |
| record_format | dspace |
| spelling | mit-1721.1/1181892022-10-01T16:34:07Z Implications of Warm Rain in Shallow Cumulus and Congestus Clouds for Large-Scale Circulations Nuijens, Louise Masunaga, Hirohiko L’Ecuyer, Tristan Emanuel, Kerry Andrew Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences Emanuel, Kerry Andrew Space-borne observations reveal that 20–40% of marine convective clouds below the freezing level produce rain. In this paper we speculate what the prevalence of warm rain might imply for convection and large-scale circulations over tropical oceans. We present results using a two-column radiative–convective model of hydrostatic, nonlinear flow on a non-rotating sphere, with parameterized convection and radiation, and review ongoing efforts in high-resolution modeling and observations of warm rain. The model experiments investigate the response of convection and circulation to sea surface temperature (SST) gradients between the columns and to changes in a parameter that controls the conversion of cloud condensate to rain. Convection over the cold ocean collapses to a shallow mode with tops near 850 hPa, but a congestus mode with tops near 600 hPa can develop at small SST differences when warm rain formation is more efficient. Here, interactive radiation and the response of the circulation are crucial: along with congestus a deeper moist layer develops, which leads to less low-level radiative cooling, a smaller buoyancy gradient between the columns, and therefore a weaker circulation and less subsidence over the cold ocean. The congestus mode is accompanied with more surface precipitation in the subsiding column and less surface precipitation in the deep convecting column. For the shallow mode over colder oceans, circulations also weaken with more efficient warm rain formation, but only marginally. Here, more warm rain reduces convective tops and the boundary layer depth—similar to Large-Eddy Simulation (LES) studies—which reduces the integrated buoyancy gradient. Elucidating the impact of warm rain can benefit from large-domain high-resolution simulations and observations. Parameterizations of warm rain may be constrained through collocated cloud and rain profiling from ground, and concurrent changes in convection and rain in subsiding and convecting branches of circulations may be revealed from a collocation of space-borne sensors, including the Global Precipitation Measurement (GPM) and upcoming Aeolus missions. Keywords: Warm rain; Shallow cumulus; Congestus; Circulations; Climate 2018-09-28T13:58:14Z 2018-09-28T13:58:14Z 2017-09 2017-02 2018-09-21T16:06:20Z Article http://purl.org/eprint/type/JournalArticle 0169-3298 1573-0956 http://hdl.handle.net/1721.1/118189 Nuijens, Louise et al. “Implications of Warm Rain in Shallow Cumulus and Congestus Clouds for Large-Scale Circulations.” Surveys in Geophysics 38, 6 (September 2017): 1257–1282 © 2017 The Author(s) https://orcid.org/0000-0002-2066-2082 http://dx.doi.org/10.1007/S10712-017-9429-Z Surveys in Geophysics Creative Commons Attribution 4.0 International License http://creativecommons.org/licenses/by/4.0/ application/pdf Springer-Verlag Springer |
| spellingShingle | Nuijens, Louise Masunaga, Hirohiko L’Ecuyer, Tristan Emanuel, Kerry Andrew Implications of Warm Rain in Shallow Cumulus and Congestus Clouds for Large-Scale Circulations |
| title | Implications of Warm Rain in Shallow Cumulus and Congestus Clouds for Large-Scale Circulations |
| title_full | Implications of Warm Rain in Shallow Cumulus and Congestus Clouds for Large-Scale Circulations |
| title_fullStr | Implications of Warm Rain in Shallow Cumulus and Congestus Clouds for Large-Scale Circulations |
| title_full_unstemmed | Implications of Warm Rain in Shallow Cumulus and Congestus Clouds for Large-Scale Circulations |
| title_short | Implications of Warm Rain in Shallow Cumulus and Congestus Clouds for Large-Scale Circulations |
| title_sort | implications of warm rain in shallow cumulus and congestus clouds for large scale circulations |
| url | http://hdl.handle.net/1721.1/118189 https://orcid.org/0000-0002-2066-2082 |
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